The artificial blood vessel is an example of the appliance to be implanted. At present, treatment of, for example, aortic aneurysm is conducted by implanting an artificial blood vessel. In particular, the portion of a blood vessel which has an aneurysm is removed by resection, and an artificial blood vessel is implanted in place of the resected portion and connected to the remaining blood vessel by suturing or the like.
The above-mentioned method of surgically implanting the artificial blood vessel for treatment of aortic aneurysm, however, is highly dangerous. Especially, an emergency operation for treatment of a ruptured aneurysm has a low life-saving rate, and an operation of dissecting aortic aneurysm is difficult to conduct and has a high death rate.
Therefore, in order to treat these diseases without a surgical operation, a method has been developed of introducing a catheter into an appliance such as an artificial blood vessel in collapsed condition into a human organ such as a blood vessel, and transporting the appliance to a desired position such as an affected or constricted portion thereof, where the appliance is released so as to be expanded and implanted there.
The appliance to be implanted is so constructed that a pair of end wire rings which are flexibly foldable and elastic are arranged to divide themselves, each of the end wire rings is connected by a tubular cover which is made of a sheet of flexible and tensile material and an intermediate wire ring is arranged between both of the end wire rings and fixedly connected to the above-mentioned tubular cover by suturing or with adhesive.
As a method of collapsing the appliance to be implanted, the following method is adopted in which a plurality of hooking means for a pull string to be passed are formed at every other dividing points each of which equally divides the circumference of the front end wire ring into an even number, the front end wire ring is folded into a wavy shape with the dividing points which are provided with a hooking means for a pull string forming forwardly directed peaks and the dividing points which are not provided with a hooking means for a pull string forming the bottoms of forwardly directed valleys, each of the intermediate wire rings and the rear end wire ring is folded into a wavy shape having the same phase as that of the front end wire ring and the whole artificial blood vessel is inserted into a catheter.
The above-mentioned intermediate wire ring is inevitable because of several points of view, such as it provides the artificial blood vessel with a capability of keeping its tubular shape so as to fit a human body when arranged at a bent position in a body, thereby to prevent the artificial blood vessel from being pushed downstream. However, if such an intermediate wire ring is attached to the tubular cover, the appliance is easily prevented from being folded. The reason is that the tubular cover tries to follow the movement of the front end wire ring with forming big wrinkles near the front end wire ring when the front end wire ring is folded into a wavy shape since the tubular cover is connected to the front and rear end wire rings at both end portions thereof. However, as the tubular cover is made of a sheet, the locally formed wrinkles do not bring about transformations at the center of the tubular cover. Therefore, for example, if the whole area of the circumference of the intermediate wire ring is fixedly connected to the tubular cover, the center of the tubular cover is dragged at the specified positions of the circumference thereof toward the direction of the peak or the valley along the wavy shape of the intermediate wire ring and the whole tubular cover tends to be bulky as well as unfavorable load is applied to the intermediate wire ring because of the sliding resistance. Therefore, the intermediate wire ring may be hindered from being folded into a small size with forming a regular wavy form because of distortion of the direction the intermediate wire ring is to be folded as well as of folding force. Even though the intermediate wire ring is fixedly connected to the tubular cover only at several points of the circumference thereof each of which is spaced apart, the points selected at random will cause sliding resistance from the tubular cover toward the peaks or valleys, thereby to provide no effective means to solve the problems.
In addition, the mutual interference between the intermediate wire ring and the tubular cover not only prevents the intermediate wire ring from being folded but also folds the appliance to be implanted imperfectly and insufficiently. Bent portion caused by the appliance to be implanted unnatuarally folded will cut off the permanent function as a blood vessel. This also may hinder the movement of transporting the artificial blood vessel through a catheter and the function of the appliance to be implanted as it is intended to because of imperfect restoration of the appliance to be implanted even though the appliance to be implanted is released at a target portion.
On the other hand, the blood vessel is distributed variously in a body and, for example, an artery which comes from a heart is bifurcated at the groin of a thigh. If an affected part falls on the bifurcated part, the above mentioned cylindrical-shaped artificial blood vessel can not be used as it is, so that it is inevitable that an artificial blood vessel whose shape fits for such a shape of blood vessel should be developed. In addition, for implanting an artificial blood vessel in such a bifurcated part it is not enough just to transport the artificial blood vessel to a target position through a catheter and release it there. In this case, it is necessary to move the artificial blood vessel to be fit for a shape of the blood vessel at an target position after released, thereby requiring to develop a method of moving the artificial blood vessel.
The object of the invention is to solve all of the above-mentioned problems.